Massive MIMO systems have got extraordinary spectral efficiency using a large number of base station antennas,but it is in the challenge of pilot contamination using the aligned pilots.To address this issue,a selectiv...Massive MIMO systems have got extraordinary spectral efficiency using a large number of base station antennas,but it is in the challenge of pilot contamination using the aligned pilots.To address this issue,a selective transmission is proposed using time-shifted pilots with cell grouping,where the strong interfering users in downlink transmission cells are temporally stopped during the pilots transmission in uplink cells.Based on the spatial characteristics of physical channel models,the strong interfering users are selected to minimize the inter-cell interference and the cell grouping is designed to have less temporally stopped users within a smaller area.Furthermore,a Kalman estimator is proposed to reduce the unexpected effect of residual interferences in channel estimation,which exploits both the spatial-time correlation of channels and the share of the interference information.The numerical results show that our scheme significantly improves the channel estimation accuracy and the data rates.展开更多
Soil enzyme activities can be used as indicators of microbial activity and soil fertility. In this paper, the activities of invertase （IA）, phosphatase （PA） and urease （UA） were investigated in tundra soils coll...Soil enzyme activities can be used as indicators of microbial activity and soil fertility. In this paper, the activities of invertase （IA）, phosphatase （PA） and urease （UA） were investigated in tundra soils collected from marine animal colonies, areas of human activity and background areas on Fildes Peninsula, maritime Antarctica. Soil enzyme activities were in the range of 1.0- 82.7 mg·kg^-1.h^-1 for IA, 0.2-8.2 mg·kg^-1.h^-1 for PA and 0.2-39.8 mg·kg^-1.h^-1 for UA. The spatial distribution patterns for soil enzyme activities corresponded strongly with marine animal activity and human activity. Significantly higher soil IA and PA activities occurred in penguin colony soils, whereas seal colony soils showed higher UA activity. Statistical analysis indicated that soil IA activity was controlled by the levels of soil nutrients （TOC, TN and TP）, PA activity was closely related with TP, and UA activity was affected by the soil pH. Overall, the deposition amount of penguin guano or seal excreta could impact the distribution of enzyme activity in Antarctic tundra soils. Multiple stepwise regression models were established between the enzyme activities, soil physicochemical properties and heavy metals Cu and Zn （[IA]=0.7[TP]--0.2[Cu]＋22.3[TN]＋15.1, [PA]=0.3[TP]＋0.03[Mc]＋0.2, [UA]=16.7[pH]-0.5[Cu]＋ 0.4[Zn]-72.6）. These models could be used to predict enzyme activities in the tundra soils, which could be helpful to study the effects of marine animal activity and environmental change on tundra ecosystems in maritime Antarctica.展开更多
基金Supported by the Program for Excellent Talents in Beijing(No.2014000020124G040)National Natural Science Foundation of China(No.61372089,61571021)National Natural Science Foundation of Beijing(No.4132007,4132015,4132019)
文摘Massive MIMO systems have got extraordinary spectral efficiency using a large number of base station antennas,but it is in the challenge of pilot contamination using the aligned pilots.To address this issue,a selective transmission is proposed using time-shifted pilots with cell grouping,where the strong interfering users in downlink transmission cells are temporally stopped during the pilots transmission in uplink cells.Based on the spatial characteristics of physical channel models,the strong interfering users are selected to minimize the inter-cell interference and the cell grouping is designed to have less temporally stopped users within a smaller area.Furthermore,a Kalman estimator is proposed to reduce the unexpected effect of residual interferences in channel estimation,which exploits both the spatial-time correlation of channels and the share of the interference information.The numerical results show that our scheme significantly improves the channel estimation accuracy and the data rates.
基金supported by the National Natural Science Foundation of China (Grant nos. 41176171 and 41076124)the Specialized Research Fund for the Doctoral Program of Higher Education (Grant no. 20123402110026)
文摘Soil enzyme activities can be used as indicators of microbial activity and soil fertility. In this paper, the activities of invertase （IA）, phosphatase （PA） and urease （UA） were investigated in tundra soils collected from marine animal colonies, areas of human activity and background areas on Fildes Peninsula, maritime Antarctica. Soil enzyme activities were in the range of 1.0- 82.7 mg·kg^-1.h^-1 for IA, 0.2-8.2 mg·kg^-1.h^-1 for PA and 0.2-39.8 mg·kg^-1.h^-1 for UA. The spatial distribution patterns for soil enzyme activities corresponded strongly with marine animal activity and human activity. Significantly higher soil IA and PA activities occurred in penguin colony soils, whereas seal colony soils showed higher UA activity. Statistical analysis indicated that soil IA activity was controlled by the levels of soil nutrients （TOC, TN and TP）, PA activity was closely related with TP, and UA activity was affected by the soil pH. Overall, the deposition amount of penguin guano or seal excreta could impact the distribution of enzyme activity in Antarctic tundra soils. Multiple stepwise regression models were established between the enzyme activities, soil physicochemical properties and heavy metals Cu and Zn （[IA]=0.7[TP]--0.2[Cu]＋22.3[TN]＋15.1, [PA]=0.3[TP]＋0.03[Mc]＋0.2, [UA]=16.7[pH]-0.5[Cu]＋ 0.4[Zn]-72.6）. These models could be used to predict enzyme activities in the tundra soils, which could be helpful to study the effects of marine animal activity and environmental change on tundra ecosystems in maritime Antarctica.
